# Trapezoidal footing | Uses, Advantages & Disadvanatges

Table of Contents

In this article we will discuss trapezoidal footing.

### ** 1. Introduction **

Trapezoidal footing is a type of footing that carries unequal loads from 2 columns when the heaviest load outside the column distance is limited.

It is used when the area of footing is fixed and the soils at the site are loose soil.

** 2. Formula for Calculating Trapezoidal Footing Volume **

As we know that, Trapezoidal footing is made by the superimposing of a rectangular cuboid and truncated pyramid as shown in the figure below.

Now,

The volume of trapezoidal footing=Volume of Rectangular cuboid (V1) + Volume of a truncated pyramid (V2)

**= V1 + V2 ** …………….(Eq.1)

I. Volume of rectangular cuboid (V1);

**= A * B * hc ** …………….(Eq.2 )

where,

A= length of the cuboid

B= Breadth of cuboid

hc= Height of cuboid

II. Volume of truncated pyramid ( V2 );

**= ht/3 * ( A1 + A2 + √(A1 +A2) ) ** ……..(eq.3)

Where,

A1= area of a bottom surface of the truncated pyramid

A2= area of the upper surface of the pyramid

ht= height of the pyramid

From equation 1,2 and 3 we can write the final formula for calculating volume of trapezoidal footing as shown below;

**= V1 + V2**

= ( A*B*hc) + ht/ 3 ( A1 + A2 + (√ (A1+A2)) )

Now ,We are going to find out the volume of trapezoidal footing shown in figure 3 as above;

i. ht=300mm = 0.3m

ii. hc=300mm=0.3m ( lets assume)

iii. Area of cuboid (A *B)= (2000mm * 1600mm) = 3.2 m²

iv. Area of bottom surface of the pyramid(A1) =3.2m²

v. Area of top surface of the pyramid (A2)= (800*800)mm^2=0.64m²

Now, **Total Volume= V1 + V2**

=( A*B*hc) + ht/ 3 ( A1 + A2 + (√ (A1+A2)) )

=(3.2 * 0.3) + 0.3/3 (3.2+0.64 +(√(3.2+0.64)))

=0.96 +0.57995

= 1.539959 m^3

The total volume of the trapezoidal footing of figure 3 = 1.5399m^3

** 3. Uses **

Trapezoidal footing is use

I. For residential house and building.

II. When load applied is uneven or unequal.

III. The soil at the site is loose.

** 4. Advantages **

a. Concrete uses are less.

b. Cheap to construct.

c. Less reinforcement is needed.

** 5. Disadvantages **

a. Good for small buildings only.

b. Chance of settlement.

c. Foundation subjected to pull out, torsion, moment.

Read More: Continuous Footing |

Read More: Shallow Foundation |

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